Medical wastes, e.g., infectious hospital medical wastes, represent a major component of hazardous wastes generated in the U.S. annually. In 2000, the U.S. generated more than 4.5 million tons of medical wastes. The method used most widely for their disposal continues to be incineration. Incineration suffers from problems of high handling, packaging and transportation costs, residual environmental pollution, high overall cost and severe local opposition. Those problems have been exacerbated by the provisions of the Clean Air Act of 1990. Alternatives to incineration, such as on-site autoclaving and shred-and-steam (with the steam generated by microwaves) suffer from similar drawbacks.
In current practice, medical wastes in hospitals, physicians' offices, medical labs, or other medical settings are currently segregated at the point of generation as “bio-medical waste”, “bio-hazard (sharps)” and regular non-infective trash. Those medical wastes are then collected and transported to a centralized facility. From there, part of the medical wastes, typically about 35%, are treated by microwave-steam methods in very large, plant-like facilities set up in large, dedicated rooms or in multiple, mobile tractor-trailers (e.g. those offered by Stericycle Inc (Lake Forest, Ill.) or Sanitec Inc (Sun Valley, Calif.)). The remaining medical waste is transported off-site, frequently to another state or province, for incineration in very large incineration facilities. The entire centralized collection methodology entails a large overhead with, e.g., specialized training required for the medical waste transporters.
What current technology lacks is a relatively small-footprint, local-area, relatively portable, relatively inexpensive, point-of-service system for remediation of the medical wastes at or close to where they are generated. Current technology also lacks the ability to treat medical wastes on site in a cost-effective and facile manner.
Microwave chemistry and biology utilize microwave radiation, frequently from domestic (2.45 GHz) microwave ovens, to take the place of heat reflux or catalysts in carrying out organic and inorganic reactions. Reactions that may take days under thermal reflux at high temperatures can be completed in under an hour and sometimes in minutes under microwave radiation.
Among the requirements for a microwave version of a conventional chemical reaction is a microwave-active solvent or reactant, or both. The requirement for microwave activity is the presence of a dipole. Thus, for instance, a Cl-benzene, which has a dipole and is thus microwave active, may be substituted as a solvent for benzene, which is microwave-inactive. A key feature of microwave reactions is complete penetration and activation of the entire reaction mass from the inside of the mass. Large reaction masses are completely penetrated with microwave energy instantly, rather than being heated “from the outside”, as in conventional heating, with the heat slowly penetrating to the interior. There is no “penetration depth” or “gradient”. Even the strongest microwave-absorbers absorb only about 15% of the total microwave radiation, the rest passing through them. Scattering from small metal components, if present, is reabsorbed by surrounding components. Due to this feature, microwave reactions do not require stirring or mixing.
It is important to recognize that microwave chemistry is not just an alternative method of heating, although rapid and penetrating heating is one of the important effects of microwaves.
Microwave radiation causes rapid rotational and rotational/vibrational activation and relaxation at the microwave frequency, e.g. 2.45 GHz or 2.45 billion times a second. This causes microwave-induced bond cleavage and rapid bringing together of activated reaction complexes. Thus, heating is just one of several effects of microwaves.
This “not just heating” effect of microwaves has been documented in innumerable literature studies of chemical reactions. For example, there are innumerable cases of, e.g., a particular chemical reaction requiring reflux at a specific temperature for, say, 36 hours, whilst a corresponding microwave reaction, verified with fiber optic sensors to occur at the very same temperature, is complete in, say, 1 hour. If the microwave effect were a pure heating effect, then the microwave reaction would also require about 36 hours, not 1 hour. Examples of reactions for which such a direct microwave-vs.-heat comparison is available are listed in detail by Lidström et al. for more than 300 specific types of microwave reactions with specific references cited. Lidström, P.; Tierney, J.; Wathey, B.; Westman, J., “Microwave Assisted Organic Synthesis—A Review”, Tetrahedron, 57, 9225-9283 (2001) and references therein; Majetich, G., Hicks, R., “The use of microwave heating to promote organic reactions”, J. Microwave Power & Electromagnetic Energy, 30, 27-45 (1995); Whittaker, A. G., Mingos, D. M. P., “The application of microwave heating to chemical syntheses”, J. Microwave Power & Electromagnetic Energy, 29, 195-219 (1994); Dauerman, L.; Windgasse, G.; Zhu, N.; He, Y., “Microwave treatment of hazardous wastes: physical chemical mechanisms”, Mat. Res. Soc. Symp. Proc., 269, 465-469 (1992); Wicks, G. G.; Clark, D. E.; Schulz, R. L.; Folz, D. C., “Microwave Technology for waste management applications, including disposition of electronic circuitry”, Microwaves III, Proc. Am. Ceramic Soc. 79 (1992); and Oda, S. J., “Dielectric processing of hazardous materials—present and future opportunities”, Mat. Res. Soc. Symp. Proc., 269, 453-464 (1992). Some examples of these include: N-alkylation (including urea and hydrazide formation); alkylation (including C-alkylation, N-alkylation); radical Michael addition; Knoevenagel, Wittig and other condensations; cycloadditions; esterification and trans-esterification; reactions with heterocycles.
The solvent medium is an important component in microwave chemistry/biology. The presence of an efficacious microwave-active solvent can be determinative of success. It is also true to say that, in spite of extensive theoretical and experimental studies, many aspects of microwave chemistry/biology are still not completely understood. For example, it is not completely understood why certain reactions progress extremely well under microwaves while others do not. Published studies that document these issues include the following: Writeups on the work of Prof. Ajay Bose's group at Stevens Institute of Technology (Hoboken, N.J.) in: Chemical & Engineering News, May 20, 1996 and Feb. 10, 1997, and refs. Therein; Bose, A. K.; Banik, B. K.; Lavlinskaia, N.; Jayaraman, M.; Manhas, M. S., “MORE Chemistry in a Microwave”, Chemtech, 27, 18-24 (1997), references cited therein; Bose, A. K.; Manhas, M. S.; Ganguly, S, N.; Sharma, A. N. and Banik, B. K. MORE Chemistry for less pollution: Applications for process development. Synthesis 2002, 11 1578-1591. Bose, A. K.; Ganguly, S, N.; Manhas, M. S.; Vidyanathan, S.; Bhattacharjee, A; Sochanchinwung, R. and Sharma, A. N. Microwave assisted synthesis of an unusual dinitro phytochemical. Tet. Lett., 2004, 45, 1179-1181; Pramanik, B. N.; Ing, Y. H.; Bose, A. K.; Zhang, L. K.; Liu, Y. H.; Ganguly, S. N. and Bartner, P. L. Rapid cyclopeptide analysis by microwave enhanced Akabori reaction. Tet. Lett., 2003, 45, 2565-2568; Pramanik, B. N.; Mirza, U. A.; Ing, Y. H.; Liu, Y. H.; Bartner, P. L.; Weber, P. C. and Bose, A. K. Microwave-enhanced enzyme reaction for protein mapping by mass spectrometry: A new approach to protein digestion in minutes. Protein Science, 2002, 11, 2676-2687; Manhas, M. S.; Banik, B. K.; Mathur, A.; Vincent, J. E.; Bose, A. K., “Vinyl β-Lactams as Efficient Synthons: Eco-Friendly Approaches via Microwave Assisted Reactions”, in “Recent Aspects of β-Lactam Chemistry”, Tetrahedron Symposia in Print, 56, 5587-5601 (2000); Bose, A. K.; Manhas, M. S.; Banik, B. K.; Barakat, K. J.; Wagle, D. R., “Microwave Assisted Rapid and Simple Hydrogenation”, J. Org. Chem., 64 (16), 5746-5753 (1999); Pramanik, B. N., Mirza, U. A., Ing, Y. H., Liu, Y. H., Bartner, P. L., Weber, P. C. and Bose, A. K. “Microwave-enhanced enzyme reaction for protein mapping by mass spectrometry: A new approach to protein digestion in minutes”. Protein Science, 2002, 11, 2676-2687; Pramanik, B. N., Ing, Y. H., Bose, A. K., Zhang, L. K., Liu, Y. H., Ganguly, S, N. and Bartner, P. L “Rapid cyclopeptide analysis by microwave enhanced Akabori Reaction.” Tet. Lett., 2003, 44, 2565-2568.
Among theories seeking to explain the unique microwave chemistry phenomenon is one that posits that extensive rotation induced by microwaves (again, 2.45 billion times a second for 2.45 GHz microwaves) leads to greater probability of collision of reactive molecules in the precise rotational conformation required for chemical reaction to occur successfully.
Peterson (U.S. Pat. No. 5,759,486) discloses an apparatus and method for microwave sterilization of medical, surgical, veterinary and dental instruments at atmospheric pressure. The apparatus uses a microwave oven, a sterilization chemical, and water. The method requires a sterilization chemical that has a boiling point greater than 100° C., and utilizes poly(ethylene glycol) (PEG). Among the possible sterilizing chemicals cited are glycerin, propylene glycol, and di(propylene glycol). Instruments to be sterilized are placed in a tray, covered with the sterilizing chemical, the tray covered and placed in microwave oven. The tray and cover can be stainless steel, glass and microwave-transparent plastics such as polyimides. The microwave oven is activated for 4 to 5 minutes. The sterilizing chemical is drained and sterile water then used to wash the instruments. The method requires the separate production of sterile water by distillation of the rinsates.
Cha (U.S. Pat. No. 6,830,662) discloses a process for microwave destruction of harmful substances such as chemical and biological warfare (“CW” and “BW”) agents as well as certain types of biological wastes such as animal remains. Acetonitrile is utilized as an example of a chemical agent that is related to a class of cyanide containing CW agents. Acetonitrile gas is passed over a carbonaceous bed containing a silica-based oxidation catalyst mixed with SiC particles. Upon directing 400 watts of 2.45 GHz microwave power at the bed, “complete destruction” of the acetonitrile is noted. In a typical, similar application to pyrolysis of solid medical waste, a two-stage reactor having carbonaceous beds is employed. In another application, sterilization of an Escherichia coli culture flowing over a bed of activated carbon, while subject to the same microwave power, was achieved rapidly.
Mednikov (U.S. Pat. No. 6,537,493) discloses an apparatus for microwave sterilization of wastes. The key feature of this invention is circular waveguides directing 2.45 GHz microwaves from opposite directions into a sterilization chamber where they “collide”. The invention uses a pressure-retaining, hermetically sealable sterilization chamber. Microwaves are used to generate steam from a liquid reservoir substantially within the chamber.
Schiffmann et al. (U.S. Pat. No. 5,811,769, U.S. Pat. No. 5,645,748 and U.S. Pat. No. 5,552,112) disclose a sterilization method and system that uses a container for containing metallic medical instruments while being subjected to microwave radiation. An enclosed outer space having a microwave-active layer is used to generate heat, which raises the temperature of an enclosed inner space sufficient for sterilization. The invention does not use water/steam, but rather relies on the maintenance of a temperature of at least 204.4° C. (400° F.) for a period of time sufficient for sterilization. Schifmann et al. (U.S. Pat. No. 5,837,977) describe a heating container with a microwave-reflective dummy load, in which a reflective inner container is contained within a microwave-transparent outer container, for use in a sterilization apparatus.
Other examples of methods and systems for remediation of medical waste include Tomasiello (U.S. Pat. No. 6,344,638 and U.S. Pat. No. 6,245,985), Held et al. (U.S. Pat. No. 5,833,922 and U.S. Pat. No. 5,709,842), Bridges et al. (U.S. Pat. No. 5,641,423 and U.S. Pat. No. 5,609,820), Held et al. (U.S. Pat. No. 5,607,612), Göldner et al. (U.S. Pat. No. 5,270,000), Katschnig et al. (U.S. Pat. Nos. 6,524,539, 5,879,643, 5,403,564, 5,407,641 and 5,246,674), Göldner (German Pat specification 3,505,570), McCullough et al. (U.S. Pat. No. 6,097,015), Wicks et al. (U.S. Pat. No. 6,262,405 and U.S. Pat. No. 5,968,400), Kutner et al. (U.S. Pat. No. 5,413,757 and U.S. Pat. No. 5,019,344), Riley (U.S. Pat. No. 5,792,421), Graves et al. (U.S. Pat. No. 6,159,422), Eser et al. (U.S. Pat. No. 5,759,488), Pearson (U.S. Pat. No. 7,028,623), Pappas (U.S. Pat. No. 5,348,235), Drake (U.S. Pat. No. 5,223,231), Varma et al. (U.S. Pat. No. 6,646,241), Uesugi (U.S. Pat. No. 5,178,828), Shieh et al. (U.S. Pat. No. 5,708,259 and U.S. Pat. No. 5,429,799), Kawashima et al. (Japanese Pat specification No. 6098930), Kamata et al. (Japanese Pat specification 7047112), Fukui et al. (Japanese Pat specification 5095992), Kameda et al. (Japanese Pat specification 5023657, Japanese Pat specification 5015866, and Japanese Pat specification 5057268), Terayama et al. (Japanese Pat specification No. 2001-314847), Kawahara et al. (Japanese Pat specification 2004-358036), Takahashi et al. (Japanese Pat specification No. 2004-181022), Kunieda et al. (Japanese Pat specification No. 2006-204374), Nakajima (Japanese Pat specification No. 3126462), Mori et al. (Japanese Pat specification No. 3068487), Won Sam (U.S. Pat. No. 5,397,551 and Canadian Pat No. 2,073,213), Schiller (German Pat specification No. 4,201,491), Marshall et al. (PCT application WO95/14,496), Hunt (U.S. Pat. No. 5,951,947), Langenegger (British Pat specification No. 2,320,247), Podzorova et al. (Russian Pat specification No. 2,221,592), Tang et al. (Chinese Pat. specification 2741684Y), Zhang et al. (Chinese Pat specification 1698984), Sin(Korean Pat specification 2006-0017907), Novak (U.S. Pat App. Pub. No. 2007/0102279 and British Pat specification No. 2,435,039), Pilema (German Pat No. 3,913,472).
However, there is still a need for a simple, inexpensive, ambient-pressure, environmentally benign, non-toxic, low-power, point-of-service method and apparatus for remediation of medical waste at or close to the point of its generation, and its further rendition into unrecognizable medical wastes suitable for disposal as ordinary refuse or “Class 10 municipal medical waste”. Thus, it is an object of the invention to provide a simple, inexpensive, ambient-pressure, environmentally benign, non-toxic, low-power, point-of-service method and apparatus for remediation of medical waste at or close to the point of its generation, and its further rendition into unrecognizable medical wastes suitable for disposal as ordinary refuse or “Class 10 municipal medical waste”.